A particular situation related to the present invention is an ultrasonic welding process. During an ultrasonic welding process, for example, in a semiconductor packaging process, conductive wire is bonded between electrical contact pads on the integrated circuit chip (die) and electrical contacts on the leadframe by using an ultrasonic transducer with frequency f (usually 30 kHz≦f≦200 kHz). The ultrasonic transducer has a wedge or capillary bonding tool affixed at the end of the transducer using a screw. It is this tool which applies the ultrasonic vibration from the transducer to the conductive wire to bond the wire onto the die pad or the leadframe. The oscillation amplitude of the bonding tool is one of the critical parameters necessary to achieve consistent bonding results because it indicates whether the tool has been mounted properly to the transducer as well as showing whether ultrasonic energy has been transmitted adequately from the transducer to the tool. Moreover, after the bonding tool has been in service for a period of time, wear and tear will occur and the bonding tool will need to be replaced. The oscillation amplitude of the bonding tool can thus be used as an indicator to prompt the operator to replace the tool in order to maintain quality of the bondings. Of course, in other situations where ultrasonic vibration devices are used, there may also exist the need for accurate and economical methods or apparatuses for measuring amplitude of the ultrasonic vibration or detecting the changes thereof.
A number of attempts have been made in recent years to develop methods to measure the oscillation amplitude of ultrasonic welding systems. However, these methods either cannot perform real-time measurement or involve complicated operations based on optical methods which are very costly. A few examples of these methods for measuring the oscillation amplitude of ultrasonic welding systems can be found in U.S. Pat. No. 6,827,247 and the references cited in it.
U.S. Pat. No. 6,827,247 discloses an apparatus for detecting the oscillation amplitude of an oscillating object. The apparatus includes an optical radiation source and a detector including first and second optical radiation sensing areas adjacent each other. The detector and the optical radiation source are adapted to be located opposite each other with the oscillating object located between the source and the detector so that the object blocks a portion of the sensing areas from receiving optical radiation from the source. A processor coupled to the detector receives first and second output signals representing the magnitude of optical radiation sensed by the first and second optical radiation sensing areas, respectively. The processor processes the first and second output signals to obtain an indication of the amplitude of oscillation of the object.
U.S. Pat. No. 6,424,407 discloses a method for determining the relative motion of a surface with respect to a measurement device comprising: illuminating the surface with incident illumination; detecting illumination reflected from the surface to form at least one detected signal; and determining the amount of relative motion parallel to the surface from said at least one detected signal, characterized in that said determining includes correcting for the effects of relative motion perpendicular to the surface.
U.S. Pat. No. 6,323,943 discloses a vibration measurement method and apparatus utilizing a self-mixing type laser Doppler vibrator meter. The vibration measurement method includes steps of: oscillating a laser beam of a predetermined wavelength and applying the laser beam to an object to be measured; mixing the reflected laser beam from the object and the oscillated laser beam for outputting a beat wave; calculating ratio of a beat wave amplitude for the turning point of the vibrating object, with respect to a predetermined reference amplitude; and calculating a displacement amount for the turning point of the vibrating object, according to the calculated ratio. This enables to detect the vibration of the object to be measured, with a high accuracy.
U.S. Pat. No. 6,181,431 discloses a nondestructive bond testing system. The system is implemented using a pulse laser that sends a single or multiple pulse(s) of controlled magnitude and bombards an object of interest causing a thermoelastic excitation response. This excitation in turn induces an ultrasonic propagation along or through the surface material. By detecting, capturing and interpreting these thermoelastic propagation signatures, the attachment condition of the joining materials is determined. The technique is a significant improvement over traditional mechanical pull, shear or contact type techniques. The techniques are implemented in automated high speed inspection systems suitable for real time manufacturing application. Particular applications include evaluating material joining in microelectronics manufacture (such as ball bonds) and thin coating processes.
U.S. Pat. No. 5,734,108 discloses a system that detects relative movement between an optical sensor unit and a set of finely spaced, parallel grid lines. Unlike prior optical line detection systems, each set of lines is applied to a surface of an object at an angle relative to movement between the optical sensor unit and the object. The system is particularly useful for monitoring rotating members, such as shafts, but is also useful with linearly moving members. In a preferred shaft monitoring application, a plurality of optical units are provided, with a plurality of corresponding sets of parallel lines at different angles on the shaft. Signal output phase differences between the optical units are compared to precisely determine movement of the shaft in seven directions of freedom, including rigid body displacement components along three translational and three rotational axes, and shaft twist. The differentially angled sets of lines may be spaced axially along the shaft or other object, or a plurality of angled line sets may be superimposed in a single location as a set of cross-hatched lines.
U.S. Pat. No. 5,623,307 discloses a system for non-destructively measuring an object and controlling industrial processes in response to the measurement in which an impulse laser generates a plurality of sound waves over timed increments in an object. A polarizing interferometer is used to measure surface movement of the object caused by the sound waves and sensed by phase shifts in the signal beam. A photon multiplier senses the phase shift and develops an electrical signal. A signal conditioning arrangement modifies the electrical signals to generate an average signal correlated to the sound waves which in turn is correlated to a physical or metallurgical property of the object, such as temperature, which property may then be used to control the process. External, random vibrations of the workpiece are utilized to develop discernible signals which can be sensed in the interferometer by only one photon multiplier. In addition the interferometer includes an arrangement for optimizing its sensitivity so that movement attributed to various waves can be detected in opaque objects. The interferometer also includes a mechanism for sensing objects with rough surfaces which produce speckle light patterns. Finally the interferometer per se, with the addition of a second photon multiplier is capable of accurately recording beam length distance differences with only one reading.
U.S. Pat. No. 5,431,324 discloses an ultrasonic bonding apparatus. The ultrasonic bonding apparatus comprises an ultrasonic wave controller, a bonding system including a bonding head, a laser oscillator, a laser optics, a vibration monitoring system including a vibrometer, and a mechanism for feeding a result of monitoring back to a bonding condition.
U.S. Pat. No. 5,199,630 discloses a method, and apparatus for performing the method, for the ultrasonic contacting wired connection of electrical circuits to metallic leadframe strips. The apparatus essentially includes a bonding head with the energy transducer located thereon for feeding to the process point of the leadframe strip and for producing a longitudinal vibration amplitude is supplied with a first voltage, the bonding head is associated a measuring head fixed to a machine base, and the measuring head has an optical/electrical sensor which measures the instantaneous amplitude of the longitudinal vibration of the infeed of the bonding head and determining a correction factor mathematically from the measured quantities obtained, and the first ultrasonic value for the vibration amplitude of the energy transducer is calibrated with the correction factor.
U.S. Pat. No. 5,101,599 discloses an amplitude control unit for an ultrasonic machine comprising a load detector for detecting the load applied to the tip of a tool during ultrasonic machining on the work, a load/amplitude conversion circuit for converting the load output detected by the load detector into an amplitude conversion value appropriate for the load at the tip of the tool, an amplitude addition circuit for receiving the amplitude conversion value generated by the load/amplitude conversion circuit and for adding it to a predetermined amplitude value at no load. The vibration of the piezoelectric transducer is changed to correspond to the load applied to the work by sending the new amplitude value generated by the amplitude addition circuit to the high frequency oscillator.
U.S. Pat. No. 4,854,494 discloses a method of monitoring bonding parameters during a bonding process. The method is based on the object of continuous monitoring of bonding parameters in order to provide adjustment of bonding machines and thereby increase the reliability of the bonded connections. A bonding force is measured by a wire strain gauge attached to a bonding arm and an ultrasound amplitude is measured by a piezo-electric sensor secured to the bonding arm. The method can be used with all bonding machines which work with ultrasound.
Citation of documents herein is not intended as an admission that any of the documents cited herein is pertinent prior art, or an admission that the cited documents are considered material to the patentability of the claims of the present application.